Reactivity of iron carbonyl complexes in a hydrated sodium-Y zeolite matrix and catalysis of the resulting hydride anion HFe3(CO)11- for water-gas-shift reaction

Abstract

Iron carbonyls Fe(CO)/sub 5/, Fe/sub 2/(CO)/sub 9/, and Fe/sub 3/(CO)/sub 12/ have been introduced into a hydrated Na-Y zeolite. Fe(CO)/sub 5/ was only weakly adsorbed on the zeolite. Fe/sub 2/(CO)/sub 9/ and Fe/sub 3/(CO)/sub 12/ were reactive in the hydrated zeolite cages to yield a hydride anion species HFe/sub 3/(CO)/sub 11//sup -/ which was characterized by IR absorption bands at 2044, 1987, 1950, and 1645 cm/sup -1/, UV-vis spectrum at 540 nm, and gas-phase analyses. The red shift of absorption band of the bridging carbonyl indicated ionic interaction of a bridging carbonyl with an Al/sup 3 +/ ion in the zeolite matrix. The formation of the anion species was not observed in a dehydrated Na-Y zeolite, indicating the importance of water or a surface hydroxyl group n the reaction. The reaction course from di- or trinuclear iron carbonyl to the hydride anion has been studied by an ESR technique. Fe/sub 2/(CO)/sub 8//sup -/, Fe(CO)/sub 4//sup -/, and Fe/sub 3/(CO)/sub 11//sup -/ species were detected as intermediates, and reaction schemes have been proposed. The resulting HFe/sub 3/(CO)/sub 11//sup -/ was stable at or below 413 K both in a vacuum or in a CO atmosphere. Above this temperature it was graduallymore » decomposed. Catalytic activity of the HFe/sub 3/(CO)/sub 11//sup -/ species was examined for water-gas-shift reaction at 333-453 K and atmospheric pressure. The activity was very high and comparable to that reported in the homogeneous phase at high pressure. Kinetics and spectroscopic studies indicated that the reaction between HFe/sub 3/(CO)/sub 11//sup -/ and H/sub 2/O would be rate-determining.« less